Studies on the Physiology of Regeneration Buds of Hordeum bulbosum

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Abstract
The regeneration buds of Hordeum bulbosum L. were found in relatively constant numbers and positions in relation to the bulbs, which are situated at the bases of flowering shoots, below the soil surface. Changes in the levels of dormancy were studied by tests of their ability to sprout and/or root when harvested at intervals during the season of dormancy. Relaxation of dromancy was associated with increase in the fraction of active bulbs, as well as in the number of active buds on each. The ability of the bulbs, as well as of the buds, to become active at low temperatures preceded their ability to do so at high ones, though temperature sensitivity was subsequently negligible. Marked positional differences found among the buds on each bulb were expressed in the extent of the morphological development of the buds, activation potential and its temperature interactions, rate of relaxation of dormancy, kinetics of activation, relationships between rooting and sprouting capacity, and changes in them during the relaxation of dormancy. The results are interpreted as indicating that an agent which induces the transformation of axillary buds into regeneration buds reaches them at or about the time of flower initiation. The positional differences reflect gradients in receptivity of the buds toward this agent, peaking in the bud on the node subtending the bulb and decreasing in progressively younger or older buds. The disappearance of temperature sensitivity with relaxation of dormancy was accompanied by a marked upward shift in the temperature optimum. The survival value of this shift under Mediterranean climatic conditions is discussed. Relaxation of dormancy is apparently a 2-stage process, the first affecting rooting and sprouting differentially, the 2nd doing so equally. Two alternative hypotheses are suggested, one involving control by 2 systems, the other by a single one. The moisture content of the bulb was a factor that determined whether its buds would become nonviable, sprout (when non-dormant), or remain viable and progress in relaxation of dormancy. Under field conditions the moisture content required for viability and relaxation of dormancy depends on a sustained supply of moisture from deeper soil layers via live roots.

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